Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion

Abstract

New CT scans of the spiral-tooth fossil, Helicoprion, resolve a longstanding mystery concerning the form and phylogeny of this ancient cartilaginous fish. We present the first three-dimensional images that show the tooth whorl occupying the entire mandibular arch, and which is supported along the midline of the lower jaw. Several characters of the upper jaw show that it articulated with the neurocranium in two places and that the hyomandibula was not part of the jaw suspension. These features identify Helicoprion as a member of the stem holocephalan group Euchondrocephali. Our reconstruction illustrates novel adaptations, such as lateral cartilage to buttress the tooth whorl, which accommodated the unusual trait of continuous addition and retention of teeth in a predatory chondrichthyan. Helicoprion exemplifies the climax of stem holocephalan diversification and body size in Late Palaeozoic seas, a role dominated today by sharks and rays.

Compound complex curves: The authentic geometry of esthetic dentistry

“…11,18 An ancient cartilaginous fish genus, Helicoprion, even had its mandibular teeth arranged in a spiral whorl. 20 Theodore Cook, in his book The Curves of Life, quoted Alfred Wallace, one of the fathers of modern evolutionary theory, as saying, "the basic condition of the exquisite forms in nature, (is) never producing straight lines but an endless variety of curves, and spirals." 3 Curves and spirals are nature's economical way of accommodating growth to produce effective functional form.…”

Eating with a saw for a jaw: Functional morphology of the jaws and tooth‐whorl inHelicoprion davisii

“…The tooth whorl has been widely depicted as spiraling upward or downward from the jaws or as defense structures emanating from dorsal fins and tail (Woodward, ; Karpinsky, , ; Simoens, ; Hay, ; John, ; Obruchev, ; Eaton, ; Bendix‐Almgreen, ; Matsen and Troll, ; Purdy, ; Carr, ). Recently, CT‐scans of a fossil Helicoprion , specimen IMNH 37899, revealed that the jaws were imbedded deeper inside the rock (Tapanila et al, ; Fig. A).…”

“…A). The jaws were articulated and surrounded the tooth whorl in a naturally closed position (Tapanila et al, ; Fig. B,C).…”

The Divination of Dentitions in Evolution

“…The extraordinary "lawn-mower" dental battery of Nigersaurus (Figure 1), adapted to an herbivorous diet is trumped for deviant dentitions by the bizarre spiral tooth whorl in the fossil Helicoprion [10] (Figure 2). …”